Wood absorbs and releases moisture in response to the humidity in its environment. What this means for furniture, especially wide table tops, is that a piece of wood expands and contracts. With table tops we usually do what’s called a breadboard end to the top which enables the top to move while also keeping it flat. You can see this movement by looking at the edge of the table where it meets the breadboard end. A wide table in a dry winter environment might move close to a ¼ inch per side. It’s not something to worry about given the ends are engineered to accommodate the movement. It’s entirely natural. When the humidity rises the table will move back out.